Conventional data networks are bumping up against physical limitations as the demand for higher bit rates increases. The physical limitations include size, thermal considerations, and transmission speed. Optical networks are becoming increasingly important as they mitigate some of the physical limitations of conductively wired (e.g. copper) networks. Highly compact optical waveguides and filters facilitate the high bit rate transmission of information within and between computers.
Conventional planar waveguide systems, typically based on air-clad, oxide-clad, or nitride-clad structures such as rectangular strip, rib, and slot waveguides, support the design, fabrication, and planar integration of the full set of photonic components required to create photonic integrated circuits (PICs) for current applications to sensing, communications, and optical networking. The bending radius of such structures varies from hundreds of microns for the lowest-loss waveguides to several microns for some of the most tightly-bending, and substantially lossier waveguides. These conventional strip, rib, and slot waveguides have been formed into rings, Archimedean spirals, and the complex waveguide delay patterns increasingly used in chip-scale photonic implementations of complex optical coding schemes such as DPSK, DQPSK, and OAM (a.k.a. spatial division multiplexing, or vortex wave multiplexing). These and other complex photonic integrated circuit layouts have all been demonstrated using conventional planar waveguides. However, waveguide size constraints in conventional PICs limits reduction of the physical dimensions of the PICs.